The current proposal is directed at an examination of the clinical course and parallel changes in immune complexes during human leukemia. Particular attention will be directed at identification of materials within circulating immune complexes in human leukemia with special reference to possible leukemic antigens detected within isolated complexes prepared by polyethylene glycol precipitations. Immune complexes will be serially studied in new patients shortly after the initial diagnosis of leukemia. SDS polyacrylamide gels will be utilized together with peroxidase-labeled antibody to human Ia antigens as well as other stem cell antigens related to the leukemic process, such as the ALL antigen. Precise insight into the relationship between elevations in circulating immune complexes and the clinical course of leukemia will be examined during the course of this study.